IPC-SM-782A-表面贴装焊盘图形设计标准.pdf.pdf - 第91页

1.0 SCOPE This subsection provides the component and land pattern dimensions for SOT 23 (small outline transistor) components. Basic construction of the SOT 23 device is also covered. At the end of this subsection is a l…

6.0 TOLERANCE AND SOLDER JOINT ANALYSIS

Figure 4 provides an analysis of tolerance assumptions and

resultant solder joints based on the land pattern dimensions

shown in Figure 3. Tolerances for the component dimensions,

the land pattern dimensions (fabrication tolerances on the

interconnecting substrate), and the component placement

equipment accuracy are all taken into consideration.

Figure 4 provides the solder joint minimums for toe, heel, and

side fillets, as discussed in Section 3.3. The tolerances are

addressed in a statistical mode, and assume even distribution

of the tolerances for component, fabrication, and placement

accuracy.

Individual tolerances for fabrication (‘‘F’’) and component

placement equipment accuracy (‘‘P’’) are assumed to be as

given in the table. These numbers may be modified based on

user equipment capability or fabrication criteria. Component

tolerance ranges (C

, and C

) are derived by subtracting

minimum from maximum dimensions given in Figure 2. The

user may also modify these numbers, based on experience

with their suppliers. Modification of tolerances may result in

alternate land patterns (patterns with dimensions other than

the IPC registered land pattern dimensions).

The dimensions for minimum solder fillets at the toe, heel, or

side (J

) have been determined based on industry

empirical knowledge and reliability testing. Solder joint

strength is greatly determined by solder volume. An observ-

able solder fillet is necessary for evidence of proper wetting.

Thus, the values in the table usually provide for a positive sol-

der fillet. Nevertheless, the user may increase or decrease the

minimum value based on process capability.

RLP No.

Tolerance

Assumptions (mm)

Solder Joint

Toe (mm) Heel (mm) Side (mm)

FPC

min J

max C

min J

max C

min J

max

200A 0.10 0.10 0.40 0.54 0.96 0.45 0.09 0.56 0.10 0.01 0.19

201A 0.10 0.10 0.40 0.54 0.96 0.45 0.19 0.66 0.10 -0.01 0.17

202A 0.10 0.10 0.20 0.53 0.77 0.28 0.26 0.58 0.10 0.04 0.21

203A 0.10 0.10 0.40 0.49 0.91 0.45 0.32 0.79 0.10 0.04 0.21

204A 0.10 0.10 0.40 0.54 0.96 0.45 0.07 0.54 0.10 0.04 0.21

205A 0.10 0.10 0.40 0.54 0.96 0.45 0.07 0.54 0.10 0.01 0.19

Figure 4 Tolerance and solder joint analysis

Wmin

Lmin

▼

Zmax

▼

/2 T

min

Zmax = Lmin + 2J

min + T

Where:

min = Minimum toe fillet

= Combined tolerances

at toe fillet

Smax

min

Gmin = Smax - 2J

min - T

Where:

min = Minimum heel fillet

= Combined tolerances

at heel fillet

/2 T

Xmax

Xmax = Wmin + 2J

min + T

Where:

min = Minimum side fillet

= Combined tolerances

at side fillet

▼

Toe Fillet

/2 T

▼

Heel Fillet Side Fillet

▼

max

min

▼

Gmin

▼

IPC-782-8-5-4

IPC-SM-782

Subject

Metal Electrode Face (MELF) Components

Date

5/96

Section

8.5

Revision

Page4of4

1.0 SCOPE

This subsection provides the component and land pattern

dimensions for SOT 23 (small outline transistor) components.

Basic construction of the SOT 23 device is also covered. At

the end of this subsection is a listing of the tolerances and

target solder joint dimensions used to arrive at the land pat-

tern dimensions.

2.0 APPLICABLE DOCUMENTS

See Section 8.0 for documents applicable to the subsections.

3.0 COMPONENT DESCRIPTIONS

One of the first active devices in packaged form for surface

mounting was the SOT device. Plastic encapsulated three ter-

minal devices with leads formed out from the body were sur-

face mounted to overcome some of the problems and difficul-

ties in handling dip transistors. In general, SOT packages are

used with diodes, transistors, and small I/O devices.

The SOT 23 package is the most common three-lead surface

mount configuration.

3.1 Basic Construction The SOT 23 package has had

several redesigns to meet the needs of both hybrid and

printed board surface mount industries. These changes

resulted in low, medium and high profile characteristics which

basically reflect the clearance that the body is from the mount-

ing surface. See Figure 1 for construction characteristics and

Figure 2 for dimensions.

3.1.1 Termination Materials Leads should be solder-

coated with a tin/lead alloy. The solder should contain

between 58 to 68% tin. Solder may be applied to the leads by

hot dipping or by plating from solution. Plated solder termina-

tions should be subjected to post-plating reflow operation to

fuse the solder. The tin/lead finish should be at least 0.0075

mm [0.0003 in] thick.

Solder finish applied over precious metal electrodes should

have a diffusion barrier layer between the electrode metalliza-

tion and the solder finish. The barrier layer should be nickel or

an equivalent diffusion barrier, and should be at least 0.00125

mm [0.00005 in] thick.

3.1.2 Marking Parts are available with or without marked

values.

3.1.3 Carrier Package Format Carrier package format

shall be according to the following: body type TO-236, 8 mm

tape/4 mm pitch.

3.1.4 Resistance to Soldering Parts should be capable of

withstanding five cycles through a standard reflow system

operating at 215°C. Each cycle shall consist of 60 seconds

exposure at 215°C. Parts must also be capable of withstand-

ing a minimum of 10 seconds immersion in molten solder at

260°C.

IPC-782-8-6-1

Figure 1 SOT 23 construction

Passivated

Semiconductor Chip

Collector lead

Bonding wire

Epoxy body

Emitter lead

Base lead

IPC-SM-782

Surface Mount Design

and Land Pattern Standard

Date

8/93

Section

8.6

Revision Subject

SOT 23

Page1of4

4.0 COMPONENT DIMENSIONS

Figure 2 provides the component dimensions for SOT 23 components.

Component

Identiﬁer

L (mm) S (mm) W (mm) T (mm) H (mm) P (mm)

min max min max min max min max max nom

SOT 23 2.30 2.60 1.10 1.47 0.36 0.46 0.45 0.60 1.10 0.95

Figure 2 SOT 23 component dimensions

2.80–3.00

▼

See profile

table

Profile Dimension TO 236 Des

Low 0.01–0.10 AB

Medium 0.08–0.13 ——

High 0.1–0.25 AA

1.20–1.40

Dimensions are in millimeters

IPC-782-8-6-2

IPC-SM-782

Subject

SOT 23

Date

8/93

Section

8.6

Revision

Page2of4